Textile fibres or filaments from synthetic polymers, particularly polyamide polymers like nylon 66 and nylon 6, and multifilament yarns melt extruded from the same polyamide polymers, are produced for apparel uses typically as partially oriented yarn (POY) and drawn yarn. POY will have an elongation to break greater than about 55% and drawn yarn will have a lower elongation. Circular is the most common cross sectional shape for each filament comprising the multifilament yarns of either type, e.g. POY and drawn yarn. Variation on the individual filament cross sectional shapes include trilobed or 6-lobed, disclosed in Japanese Kokoku patent document 01-20243 (Nihon Ester KK), the scalloped oval cross section as disclosed by in U.S. Pat. No. 5,834,119 (Roop) and hollow polyamide filaments with a single longitudinal void, disclosed in U.S. Pat. No. 5,604,036 (Bennett et al.).
All of the foregoing examples are known variants of profiled cross sectional shaped POY and drawn yarn. Filaments with cross sectional shapes other than circular provide multifilament yarns for fabrics and garments with varied visual aesthetics, opacity and cover and lighter weight. Yarns from hollow filaments, for example the yarns of the last mentioned United States patent; provide lighter weight fabrics and garments and enhanced heat retentive properties versus conventional circular filaments, without a longitudinal void. Hollow filament yarns are particularly suited for apparel applications when textured by the conventional processes, e.g. air jet texturing (AJT) and false twist texturizing (FTT) to obtain bulky yarns. Hollow flat yarns for direct use in weaving applications are also known.
Both partially oriented and flat nylon yarns in a high void volume hollow are disclosed by Bennett et al. However, filaments with longitudinal voids are difficult to close perfectly at spinning, and may also deform substantially during the texturing process. This may result in a letter ‘C-shaped’ filaments and/or collapsed tube cross sectional shapes. Letter C-shaped filaments are able to pack closely together with a loss of open space among neighbouring filaments. In addition, letter C-shaped cross sectional filaments and collapsed tube cross sections lead to undesirable yarn and fabric properties as a result of such occurrences. Increased fabric density and diminished heat retention of the fabric and garments are among the undesirable properties. Furthermore, yarns from filaments with varied amounts of ruptured longitudinal voids contribute to dyed fabric streakiness and the intact filament voids provide opportunistic bacteria with a place to flourish.
It has now been found that the above-enumerated disadvantages can be overcome by the production of polymer filaments having a novel cross-section.
The present invention provides a profiled filament from synthetic polymer having an “open hollow” cross-sectional shape normal to the longitudinal axis of the filament. The cross-section is dimensioned to prevent a first filament from interlocking with a second filament having the same cross-section. This means a region proximate to each tip of the cross-section is wider than a spacing between said regions defining an opening to the open hollow cross-section.
The profiled cross sectional shape filaments of the invention are provided by the novel shape and design of the extrusion capillary. The filaments of this invention are prepared directly by melt extrusion of synthetic polymer through a multi-capillary spinneret plate. The term “open hollow” denotes a generally C-shaped or U-shaped cross-section having a hollow center, and a solid region defining wall portion extending around the hollow center to enclose the hollow center, but with an opening in one side of the wall linking the center to the outside of the filament. The opening is narrower than the diameter of the hollow center, thereby forming a throat or constriction between the hollow center and the outside of the filament.
Preferably, the filament comprises a solid part substantially enclosing a central hollow region. An opening leads from the exterior of the filament into the central hollow region. The solid part includes legs that terminate in feet. Confronting surfaces of the feet define the throat (the narrowest dimension) of the opening. The throat of the opening subtends a radial angle alpha (α) of not more than 90°, more preferably not more than 75° and most preferably from 10° to 60°. As seen in FIG. 1, the radial angle alpha (α) is that angle defined between two rays R1 and R2 originating at a point C. The point C is that point lying on the interior surface of the solid part of the filament that lies farthest from a reference line R3 tangentially connecting the tips of the feet. Each ray R1, R2 extends from the point C and lies tangent to a point on the confronting surfaces of the feet defining the throat of the opening D. The solid part subtends a radial angle equal to 360° minus angle alpha (360°-α). Preferably, the solid part of the cross-section subtends a radial angle of at least 270°. More preferably the solid part subtends a radial angle of at least 300°.
The filaments according to the present invention are adapted to prevent inter-engagement or stacking of the filaments. For example, hook-like engagement of two cross sections arising from insertion of an end of the solid part of a first filament cross-section through the opening in the cross-section of a second filament is prevented. This provision can be achieved as already described, by making the solid portion of the cross-section subtend a large radial angle, whereby the opening in the filament cross-section is very small. Alternatively or additionally, the ends of the solid part of the cross section may be enlarged to inhibit insertion into the opening of other filaments.
The solid portion of the cross-section in the filaments according to the present invention may form a single continuous curve. Preferably, the cross-section comprises a “central arcuate” or base portion having first and second ends and two side or “leg” portions. The leg portions extending in substantially side-by-side relationship from the first and second ends of the central arcuate portion.
In preferred embodiments, such as the filament cross section geometry shown in FIG. 1, the filament cross sectional shape is characterized by a central arcuate portion 1 (extending horizontally in FIG. 1) and first and second, generally parallel, elongated leg portions 2, 3 (extending vertically in FIG. 1) joined to the central arcuate portion. The distal portion of each leg (2, 3) opposite the juncture with the central arcuate portion 1 defines an enlarged foot portion 4. Each foot portion 4 is characterized by dimension F, the length of the foot, as shown in FIG. 1. The profiled filament cross-section is open in the center. This open portion is bounded on three sides by the leg portions 2, 3 and central arcuate base portion 1. The feet portions 4 are oriented in a substantially side-by-side relationship defining an aperture between confronting surfaces of the foot portions with dimension D leading to the open portion, as shown in FIG. 1. The dimension D is less than dimension F. As a result, any foot on any leg of the profiled filament is sufficiently large with respect to the aperture between the pair of legs on any other identical filament to prevent a foot of the first filament from being accommodated (interlocked) between the legs of the other filament in a multifilament yarn bundle, as illustrated by FIG. 2.
Preferably, the polymer used to form the profiled polymer filament according to the present invention is a polyamide. More preferably, the polyamide polymer has a relative viscosity, by a formic acid method, greater than 40, and still more preferably the relative viscosity of the polyamide by a formic acid method is in the range of 46 to 56. Preferably, the polyamide is selected from the group consisting of nylon 66 and nylon 6 and copolyamides.
Preferably, the single filament linear density is from 0.5 to 20 dtex, and more preferably it is from 2 to 10 dtex. Most preferably it is less than 4 dtex. Preferably, the filament cross-sectional shape is substantially constant along the length of the filament. Preferably, the filament non-uniformity is less than 1 Uster %.
The profiled filaments according to the present invention provide a lighter unit weight yarn, particularly after texturing by AJT (air jet texturizing) or FTT (false twist texturizing). The yarn incorporates high free volume of air space. The volume of air space contributes to enhanced thermal retention of fabrics and garments produced from the yarn. The yarn when knitted or woven into fabrics provides a less dense fabric than similarly constructed fabrics from solely circular cross section filaments. Furthermore, the yarn exhibits a high moisture wicking capacity.
Accordingly, the present invention further provides a multifilament yarn comprising at least a portion of the profiled filaments according to the present invention.
Preferably, the yarn comprises at least 10% by weight of the profiled filaments according to the present invention, more preferably at least 25% of such filaments, still more preferably at least 50% of such filaments and most preferably it consists essentially of such filaments.
The present invention further provides an article comprising at least a portion of the yarn according to the present invention. Preferably, the article comprises a textile fabric that is knitted or woven from a yarn according to the present invention.
A further aspect of the present invention is a spinneret for the production of the profiled open hollow filaments according to the present invention by melt extrusion of polymer into filaments. The spinneret comprises a plate having upper and lower surfaces connected by an assembly of capillaries. The shape, size and configuration of the capillaries are adapted to the melt spinning of filaments according to the present invention. Specifically, either each capillary comprises two adjacent segments as in FIG. 3a, whereby the open hollow filament cross section longitudinal to the axis of the filament is obtained as the molten polymer streams from each segment coalesce at a point between the segments or each capillary has an open hollow transverse cross-section as in FIG. 3b. 
The preferred spinneret plate for the production of the profiled open hollow filaments is one with each capillary comprised of two segments in FIG. 3a. Each segment is comprised of a straight length portion 30 having at each end a junction with a pair of projecting portions. At the first end, the pair of projecting portions are of equal area and each comprise a straight portion 31, 32 terminating in a round portion 33, 34. At the second (opposite the first) end, are a pair of unequal area projecting portions. The first unequal area projecting portion is comprised of straight portion 35 and round portion 36 and the second unequal area projecting portion is comprised of straight portion 37 and round portion 38. Therefore, each segment of the capillary has three equivalent projecting portions, two on one end and one on the opposite end. The unique (longer) projecting portion present on each segment is comprised of straight portion 37 and round portion 38. Preferably, each capillary segment is the mirror image of the other segment. More preferably, each segment is the nonsuperimposable mirror image of the other segment, for example as illustrated by FIG. 3a. The nonsuperimposable mirror image relationship means that each segment possesses handiness in the same way as do human left and right hands.
The open hollow filament cross section normal to the longitudinal axis of the filament is obtained as the molten thermoplastic polymer streams from each capillary segment coalesce at a point between projecting portions of the two segments. That is, the open hollow filament cross section of the invention is formed as the molten polymer stream coalesces between confronting round portions 38 of the left and right capillary segments shown in FIG. 3a. 
In the case where the capillaries themselves have an open hollow cross-section, the capillary illustrated by FIG. 3b is a preferred spinneret geometry cross section for the production of profiled open hollow filaments. Each capillary has a cross sectional shape comprising a first straight portion 40 with a first end and a second end, opposite each other. Bifurcating from the first end of the first straight portion 40 are a second straight portion 48 and a third straight portion 50. The second straight portion 48 terminates in a round portion 49 and the third straight portion 50 extends to a point of bifurcation; wherein a fourth straight portion 53 and a fifth straight portion 52 extend from this point of bifurcation. The fourth and fifth straight portions having unequal areas and each terminate in round portions 54 and 51. Similarly, bifurcating from the second end of the first straight portion are a sixth straight portion 41 and a seventh straight portion 43. The sixth straight portion 41 terminates in a round portion 42 and the seventh straight portion 43 extends to a point of bifurcation;                wherein an eighth straight portion 46 and a ninth straight portion 44 extend from said point of bifurcation, the eighth and ninth straight portions having unequal areas and each terminate in round portions 45 and 47.        
In a further aspect, the invention provides a process for making drawn yarns and partially oriented yarns (POY) with a modified filament cross section according to the present invention. Generally, the process comprises extruding a polyamide melt, typically nylon 66 or nylon 6, of 40 to 60 RV (measured in formic acid), and preferably 48 to 52 RV to form a plurality of filaments. The spinneret according to the invention is maintained at a temperature selected from the range 245 to 295° C., more preferably it is 280° C. Multiple filaments extruded through the spinneret are cooled in a cross flow of air to form solid filaments. These filaments may be treated with oil, converged, interlaced and drawn, or remain undrawn, prior to winding up a multifilament yarn at a speed greater than 3000 meters per minute (m/min).
Referring now to the process schematic in FIG. 5, a drawn yarn is prepared by following path A. The melted polymer 10, a polyamide, is pumped to the spin pack 20 and forced through spinneret plate 30 to form filaments 40. The emerging filaments are cooled by a cross flow of air 50, having an air velocity of about 0.15 to 0.5 meters per minute. The cooled filaments are converged into a yarn 60, and an oil and water finish is preferably applied to the resulting yarn bundle at 70. The yarn 60 is forwarded through a first air interlace jet 80 to become intermingled yarn 90. Yarn 90 is forwarded to a first godet 92 (the feed roll) and its associated separator roll, wrapping several times to prevent slippage, and then to a second godet 94 (the draw roll) and its associated separator roll. The draw roll 94 is moving at a surface speed of 60 to 100%, preferably 80%, greater than that of the feed roll 92. The yarn bundle is thereby drawn (elongated), preferably by a total factor of about 1.8, reducing the overall yarn titer to form yarn 100. The drawn yarn 100 is preferably treated by a relaxation device 110 to set the draw and to relax the yarn as is conventionally practised in the art. Any known relaxation device may be employed, including steam, heated fluid, hot tube, hot shoe, heated rolls. The relaxed yarn bundle 120 is optionally passed through a second interlace jet 130 and optionally oiled before the relaxed yarn 140 is wound up on a tube 150 at a winding speed greater than 3000 meters per minute, more preferably about 3800 meters per minute. The resulting drawn yarn has an elongation of 25 to 45%, preferably 40 to 45%, and a tenacity of 35 to 45 cN/tex.
Alternatively, referring now to the process schematic in FIG. 5, a partially oriented yarn (POY) is prepared by following path B. The melted polymer 10, a polyamide, is pumped to the spin pack 20 and forced through spinneret plate 30 to form filaments 40. The emerging filaments are cooled by a cross flow of air 50, having an air velocity of about 0.15 to 0.5 meters per minute. The cooled filaments are converged into a yarn 60, and an oil and water finish is preferably applied to the resulting yarn bundle at 70. The yarn 60 is forwarded through a steam atmosphere containing interfloor tube 75, as is known in the art. The steam treated yarn 85 is intermingled at 80 partially wrapped around godet 82 and godet 84, which control any variations in winding tension the yarn may experience. The yarn 115 is wound up as a package of yarn on tube 160 at a speed of about 3800 meters per minute. The POY produced preferably has an elongation of 55 to 85%, preferably 75%, and a tenacity of 25 to 40 cN/tex, preferably about 30 cN/tex.